From: Treena Joi (tjoi@stanfordalumni.org)
Date: Fri Apr 02 2004 - 16:23:13 PST
Date: Fri, 02 Apr 2004 16:23:13 -0800 From: Treena Joi <tjoi@stanfordalumni.org> Subject: physcial change & why CO2 douses flames Message-ID: <582iDcaXN7632S16.1080951793@uwdvg016.cms.usa.net>
Two questions ...
First ... boiling point and melting point are physical properties of
chemicals ... is that correct? They only involve a phase change .. so
that would make sense .. if not .. why?
From that, I did the chemistry in a bag thing and the teacher notes say
that calcium chloride and water evolve heat, yes, which is exothermic,
going on to say it is only a physical change ...
How does that work? The salt lowers the freezing point of water ... is
that how to explain it? hence the first part of the question ... so, how
do I convince the kids of that?
I took the solution and I am letting the water evaporate off over the
weekend .. hopefully there will be salt, that is convincing .. but the
heat thing is hard to explain away .. it's a new thing, chemical changes
involve the formation of something new .. heat is not matter, that helps,
but it is just counterintuitive.
Second question
It would be great to know how exactly carbon dioxide inhibits flame
or sort of readers digest exactly
I guess I thought of a third question .. with the Rutherford Rollers
activity I am able to be more convincing about atomic structure
consisting of so much space, but then they want to know where the alpha
particles came from and how to shoot them, even how to detect them .
I assumed that charges are involved in getting alpha particles to go from
one place to another, like a cathode ray tube ... but now that wouldn't
allow for the detection of the particles on both sides of the beam ...
anyway .. any easy answers for that? My kids are in 6th grade ... so I
am trying not to get too deep
Treena Joiful
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